One of my personal Eureka moments came many years ago when I discovered the mitochondria, the tiny structures that produce the energy used within our cells. Mitochondria have DNA of their own—separate from the DNA in each cell’s nucleus. In humans, and most other species that have mitochondria, these structures are passed on to offspring exclusively from the mother. Hence, tracking mitochondrial DNA, we can search ever backward in time tracing the maternal line. We haven’t found Eve yet, but it may be possible. Adam is quite untraceable.
This came to mind yesterday when I read about claims (still not fully accepted) that the caterpillar and the butterfly that it becomes may be of two different species that once joined forces for a kind of biological tour de force. My mitochondrial encounter years ago suggested to me that bodies are chemical civilizations—imperfectly uniting quite diverse strands of living things—and indeed coexisting only because they are a kind of community of separates rather than a seamless whole. Humans can only digest, for instance—and therefore live—because we host a diverse community of bacteria.
Our bodies, of course, do not remain the same even from day to day. Yesterday we retrieved all or most of our photo albums. Some of them have photos that go back to the nineteenth century. Pictures of ourselves show the enormous changes that have taken place in our own bodies—which in turn, all these impressions, shaken well in a blender, made me wonder what identity means—and how it might be located.
Amusingly that word, identity, derives from the Latin phrase idem et idem, best translated into our own “same-old, same-old.” Thus identity is sameness. But in the physical world nothing is ever, strictly speaking, the same—not even that hard, attractive spoon I use to stir the coffee which, by chance, we “abstracted” from a house we rented in Florida three years ago. Even that spoon has lost some mass in the meantime.
If we cling strictly to a materialistic explanation of identity, it turns out that the best explanation for identity is statistical. I am statistically much the same today as yesterday, and never mind the 50 to 70 billion cells that died since 10:23 yesterday, which—thanks to Summer Time’s arrival (even time changes)—is 11:23 today.
Approximation must suffice to locate identity in time and space; to locate it absolutely we must leave the reservation and, having reread Plato’s Phaedo, we must start to feel familiar with the concept that the human self is immaterial and indestructible; its relationship to DNA, cellular or mitochondrial, is rather loose and tentative. Which suggests the happy thought that when our next caterpillar breaks is chrysalis and emerges as a butterfly, a single gorgeous soul will flutter away even if generated by two species in cooperation.